The capability for 3-D imaging of teeth and intra-oral structures in general can help to improve dental care and diagnosis and to provide more accurate data for preparation of dental appliances and prosthetics. Although there have been a number of proposed solutions to this problem, inherent difficulties with each of these approaches limit their usability, accuracy, and cost-effectiveness.
One conventional type of approach that has been proposed is contour or fringe projection imaging. Fringe projection imaging uses patterned or structured light to obtain surface contour information for complex structures of various types. In fringe projection imaging, a pattern of lines of an interference fringe or grating is projected toward the surface of an object from a given direction. The projected pattern from the surface is then viewed from another direction as a contour image, taking advantage of triangulation in order to analyze surface information based on the appearance of contour lines. Phase shifting, in which the projected pattern is incrementally spatially shifted for obtaining additional measurements at the new locations, is typically applied as part of fringe projection imaging, used in order to complete the contour mapping of the surface and to increase overall resolution in the contour image.
Fringe projection imaging has been used effectively for surface contour imaging of solid, highly opaque objects and has been used for imaging the surface contours for some portions of the human body and for obtaining detailed data about skin structure. However, technical obstacles such as tooth translucency, light scattering, and high reflection levels complicate the surface reconstruction problem and limit effective use of fringe projection imaging of the tooth. Techniques to compensate for these problems, such as temporarily coating teeth surfaces to condition the tooth surface and enhance tooth opacity for example, add time and cost to the imaging process and can tend to mask other problems.
Other methods for intra-oral 3-D imaging include depth measurement using a hand-held optical probe, such as that described in U.S. Pat. No. 5,440,393 entitled “Process and Device for measuring the dimensions of a space, in particular a buccal cavity” to Wenz. Such devices, however, are limited to making very specific measurements and are not designed for 3-D imaging of the tooth surface for one or more teeth. Confocal imaging methods, such as taught, for example, in U.S. Pat. No. 6,697,164 entitled “Imaging a Three-Dimensional Structure by Confocal Focussing an Array of Light Beams” to Babayoff et al., illuminate a discrete number of spots on the tooth surface and use this sampling to map surface contour. However, a confocal approach of this type requires a relatively complex arrangement of illumination and sensing components. Moreover, the resulting surface contour information, once obtained, must then be correlated or registered to the tooth image itself in a separate processing operation.
Among the challenges faced by dental 3-D imaging systems are the highly pronounced contours of the tooth surface. It can be difficult to provide sufficient amounts of light onto, and sense light reflected back from, all of the tooth surfaces. The different surfaces of the tooth can be oriented at 90 degrees relative to each other, making it difficult to direct enough light for accurately imaging all parts of the tooth.
It can be appreciated that an apparatus and method that provides accurate surface contour imaging of the tooth, without the need for applying an added coating or other conditioning of the tooth surface for this purpose, would help to speed reconstructive dentistry and could help to lower the inherent costs and inconvenience of conventional methods for obtaining surface contour information, such as those for obtaining a cast or other surface profile for a crown, implant, or other restorative structure.